The present invention relates to an optical measuring apparatus, and more particularly to a self-scanning type optical measuring apparatus which is used to measure a dimension, a shape and the like of an object to be measured.
Recently, various optical measuring apparatus have been developed and known in the art in which optical instruments are employed. The optical instrument usually employs a self-scanning type photoelectric conversion element including a photoelectric conversion element array which is composed of a plurality of individual photoelectric detecting elements. The photoelectric conversion element is arranged at a position equivalent to the detecting plane. An object to be measured is scanned by a parallel light beam, and thereby the photoelectric detecting elements are optically scanned to obtain electrical values corresponding to the dimension and the shape of the object to be measured. In the measurement of the dimension and the shape of the object by the optical scanning, the most basic and important problem is to obtain a parallel light beam.
FIG. 5 shows a typical example of the prior art optical measuring apparatus which employs a self-scanning type optical measuring instrument. As is shown in FIG. 5, the optical measuring apparatus comprises a light source in the form of a laser light generator 1, a fixed mirror 2 positioned on a light path of laser light generated by the laser light generator 1 and inclined at a predetermine angle with respect to the light path, a polygon mirror 3 positioned on a light path of a reflecting light beam from the fixed mirror 2, a drive motor 4 rotating the polygon mirror 3, a collimating lens 5 provided at a reflecting light path side of the polygon mirror 3 and spaced apart at a focal length f from the polygon mirror 3, a focussing lens 6 arranged at a predetermined distance from the collimating lens 6, a photoelectric conversion element 7 receiving rays of light focussed by focussing lens 6, a processing section 8 for processing an electrical signal produced by the photoelectric conversion element 7 and a displaying section 9 for displaying a dimension of an object m to be measured based on a processed signal of the processing section 8.
In accordance with the optical measuring apparatus of FIG. 5, the laser light beam produced by the laser light generator 1 is reflected by the fixed mirror 2. The reflected light beam is incidenced on the polygon mirror 3 and is further reflected by the polygon mirror 3. The reflecting light beam from the polygon mirror 3 is incidenced on the collimating mirror 5. The incidencing light on the collimating lens 5 is converted to a parallel light beam. The parallel light beam from the collimating lens 5 is focussed on the photoelectric conversion element 7 by means of the focussing lens 6.
When the polygon mirror 3 is rotated by the drive motor 4, the reflecting angle of the reflecting light beam from the polygon mirror 3 is varied according to the rotation angle of the polygon mirror 3, resulting that a scanning region a is decided. The object to be measured is scanned by the parallel light beam, and a shield portion is formed on the photoelectric element 7, during the parallel scanning light beam incidences to the object m. The photoelectric conversion element 7 generates an electrical signal corresponding to the shadow portion. The electrical signal produced by the photoelectric conversion element 7 is processed by the processing section 8 and the dimension of the object m is displayed on the displaying section 9 according to the electric signal from the processing section 8.
As mentioned above, the laser light beam is incidenced on polygon mirror and is diffused by the polygon mirror. The diffused light is made the scanning light beam by the collimating lens, and the electric signal is produced from the photoelectric conversion element according to the shadow portion formed thereon and is processed by the processing section.
Problems associated with the prior art optical measuring apparatus reside in that the apparatus was costly and large size, since the apparatus required an expensive polygon mirror and an expensive collimating lens, and the distance between the polygon mirror and the collimating lens must be set to four to five times of a scanning region. In addition, the circuitry of the processing section was complicated and expensive, since the compensation of the aberration of the collimating lens and the compensation of the trigonometric function were required as well as a precise number of rotation of the drive motor is required in order to obtain the accuracy of the measuring value.